It is desirable to monitor the biological functions (such as heart rate) of a fetus continuously during labor and delivery in order to detect fetal distress. Devices which are external to the mother's body are insufficiently sensitive. In the case of heart rate signals, such devices do not adequately isolate the fetal and maternal heartbeats. Consequently, devices which attach directly to the fetus during labor are used. U.S. Pat. No. Re. 28,990, issued to Hon et al., discloses a fetal spiral electrode assembly historically used to monitor fetal heart rate during birth.
The conventional fetal spiral electrode assembly includes a curved guide tube of adjustable shape for insertion of the fetal spiral electrode through the mother's cervix and into contact with the fetus during labor. A nonconductive plastic tip or holder is slidably received in the guide tube. A sharp, pointed, fetal spiral electrode is mounted on the forward end of the holder for contacting the fetal epidermis.
A reference (maternal) electrode in the form of a flat fin or plate is electrically isolated from the fetal electrode and located on the rear end of the holder. A flexible, hollow drive tube with a cutout on its forward end fits inside the guide tube and engages the holder. The drive tube has a diameter smaller than the diameter of the guide tube. The cutout of the drive tube engages the reference electrode in the holder to impart translation and rotation to the holder and, hence, to the fetal spiral electrode. A handle on the opposite end of the drive tube allows the user to push, pull, and rotate the drive tube within the guide tube. A forward-twisting force is applied to the drive tube to affix the fetal spiral electrode in the fetal epidermis.
The two electrodes are connected to separate wires which are threaded through the common center of the drive and guide tubes until they ultimately exit at the rear end of the drive tube. The wires connected to the electrodes are twisted about each other so that any induced voltages caused by external electromagnetic interference will be the same in each and therefore will not adversely affect the measurement of the galvanic potential difference between the electrodes. After the fetal spiral electrode is secured to the fetal epidermis, the drive tube and guide tube are removed by pulling the tubes longitudinally over the wires and away from the mother. Removal of the drive and guide tubes leaves the electrodes, the holder, and the wires in place inside the mother. The bare, uninsulated ends of the wires are then connected, via an intermediate support or leg plate, to a fetal monitor.
To use the fetal spiral electrode product, the shape of the guide tube is adjusted and the guide tube is inserted through the mother's cervix and into contact with the fetus. Once the guide tube contacts the fetus (and is held against the fetus using one of the user's hands), the drive tube is advanced (using the second hand) until the fetal spiral electrode contacts the fetus. While pressure is maintained against the fetus by the guide tube and drive tube, the drive tube is rotated, using the second hand and the handle, until the fetal spiral electrode is secured to the fetal epidermis. Typically, one full revolution suffices to secure the fetal spiral electrode. Then the drive tube and guide tube are removed by sliding them over the electrode wires.
U.S. Pat. No. 5,680,859 issued to Urion et al. is an improvement over the device disclosed in the '990 patent. Manual connection of the uninsulated ends of the wires is cumbersome and risks shorting the wires. If shorted, the wires cannot transmit correct signals from the fetal and reference electrodes. Accordingly, the '859 patent adds a connector to the wire ends of the fetal spiral electrode assembly disclosed in the '990 patent.
FIG. 6 is a side view of the fetal spiral electrode system 110 disclosed by Urion et al. Electrode system 110 includes a sharp, pointed fetal spiral electrode 120 for contacting the fetal epidermis; a reference (maternal) electrode 122 in the form of a flat fin or plate which is electrically isolated from fetal spiral electrode 120; a holder 124; and two electrode wires 126a and 126b.
Holder 124 is an electrically insulating plastic and is adapted to be slidably received inside an introducer 140. Fetal spiral electrode 120 is mounted on the forward end of holder 124. Reference electrode 122 is attached to the rearward end of holder 124.
A drive rod 130 is slidably received in introducer 140. Drive rod 130 has a clutch 128 at its forward end. Clutch 128 engages reference electrode 122 in holder 124 to impart translation and rotation to holder 124 and, hence, to fetal spiral electrode 120. A handle 150 on the opposite end of drive rod 130 allows the user to push, pull, and rotate drive rod 130. Drive rod 130, clutch 128, and handle 150 are integrally molded together.
Electrode wires 126a and 126b are separately coupled to respective electrodes 120 and 122. Electrode wire 126a (typically green in color) connected to fetal spiral electrode 120 and electrode wire 126b (typically red) connected to reference electrode 122 form a twisted wire strand 118 which extends from electrodes 120 and 122 along the entire length of drive rod 130 and handle 150. A retainer 166 is provided near the end of handle 150 opposite drive rod 130. Retainer 166 locks wire strand 118 in a fixed position. The ends of wires 126a and 126b opposite holder 124 terminate in a male connector 132.
Turning to FIG. 7, wires 126a and 126b (which are typically about 450 mm or 18 inches in length) are provided with an untwisted length 116 along a short distance (25-50 mm or 1-2 inches) of wire strand 118. Untwisted length 116 allows the clinician to separate wires 126a and 126b without cutting them. The individual wires 126a and 126b are separately connected to first and second terminal (or ring) contacts 134 and 136 in connector 132. Contacts 134 and 136 are electrically and physically separated by a spacer 138. Connector 132 has a forward tapered tip 142 which plugs into a longitudinal passage in the end of handle 150 (connector 132 is shown plugged into the passage in FIG. 6).
Connector 132 is designed to be inserted into a support or leg plate 170 which is affixed to the mother (typically to the thigh). Support plate 170 is connected, via a cable 176, to a monitor 178. Upon insertion of connector 132 into the opening of support plate 170, ring contacts 134, 136 on connector 132 click into physical and electrical contact with two corresponding barrel contacts in support plate 170. Moreover, tip 142 of connector 132 abuts a wall in support plate 170 to prevent over-insertion of connector 132.
Support plate 170 carries its own ground electrode 180. Insertion of connector 132 in support plate 170 connects electrodes 120 and 122 to monitor 178. Consequently, three electrical circuit paths are created upon interconnection of connector 132 of fetal spiral electrode system 110 and support plate 170: (1) fetal electrode 120 to green wire 126a to terminal 134 to a first barrel contact to a first output terminal to monitor 178; (b) reference electrode 122 to red wire 126b to terminal 136 to a second barrel contact to a second output terminal to monitor 178; and (c) ground electrode 180 to a third output terminal to monitor 178.
Connector 132 has a grip 144 with an ergonomically designed shape to permit the user to grasp it easily and to ensure a proper, sealed connection of connector 132 to support plate 170. Grip 144 also acts as a strain relief element through which twisted wire strand 118 enters connector 132. The diameter of connector 132 changes, at a shoulder 146, from a smaller diameter plug 148 to larger diameter grip 144. The length of smaller diameter plug 148 is selected to correspond to the length by which connector 132 must be inserted fully into support plate 170 to assure optimal signal quality. Thus, connector 132 permits a visual indication of full attachment of connector 132 to support plate 170.
Connector 132 solves the problem of manual connection of the uninsulated ends of the electrode wires. But the connector 132 with its exposed first and second terminal (or ring) contacts 134 and 136 does not prevent entirely the risk of accidental electrocution of patients by having an exposed contact engage a hazardous voltage. Such prevention is not only desirable, it is now mandated by the U.S. government and by international standards.
The "Performance Standard for Electrode Lead Wires and Patient Cables" of the Code of Federal Regulations, Chapter 21, Part 898, states that, beginning on May 9, 2000, all fetal scalp electrodes and associated cable systems must comply with the standard. In summary, this performance standard is designed to prevent accidental electrocution of patients by precluding an exposed lead or contact that might come into contact with a hazardous voltage. Consequently, leads and contacts must be constructed to prevent accidental patient contact with hazardous voltages and, after May 9, 2000, unprotected electrode lead wires and cables cannot be manufactured, distributed, or sold in the United States. Existing leads and contacts on fetal spiral electrode products currently sold in the United States market are non-compliant because the leads and contacts are exposed. Specifically, the current fetal spiral electrode designs have either two bare wires or exposed contacts that could potentially come into contact with an electrical source when not connected to the support or leg plate.
If a lead or contact may be placed on a conductive surface or inserted into an electrical socket, hazardous voltages could occur. Alternatively, if a user can run a finger over the lead or contact and can touch metal, the lead is considered non-compliant under the governmental standard. For a lead or contact to comply with the standard, it must preclude contact with hazardous voltages and pass specific tests.
There are approximately 45,000 fetal monitors in the United States and approximately three million fetal spiral electrodes are used per year. The deficiencies of the conventional devices and the market demand show that a tremendous need exists for an improved fetal spiral electrode interconnect system that functions to electrically and mechanically connect the conventional twisted wire pair with the cable to the remote fetal monitor. To overcome the shortcomings of conventional fetal spiral electrode systems, an integrated fetal electrode sleeve and wire system is provided. The principal object of the present invention is to provide an improved system that is fully compliant with governmental performance standards. An important related object is to provide a system that reduces safety risks, especially the risk of inadvertent connection to an electrical source. Another object is to provide a system that provides both safe and reliable tracing of fetal heart rate to help caregivers deliver the best patient care.